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Simultaneous Removal of Nitrogen and Phosphorus from Stormwater by Zero-Valent Iron and Biochar in Bioretention Cells

The transportation sector is frequently identified as a significant, if not primary, source of nutrients (nitrogen and phosphorus) to receiving waters. To achieve increasingly stringent regulatory requirements with existing technologies requires purchase of more real estate for stormwater treatment at considerable expense. To ameliorate this problem, the project will evaluate two waste products, biochar and zero-valent iron (ZVI), as amendments to soil media in bioretention systems. Previous laboratory studies have shown that each amendment alone is capable of removing or transforming nitrogen or phosphorus compounds. The project postulates that treatment efficiency can be enhanced considerably by combining biochar and ZVI, which would result in smaller land requirement to achieve a prescribed level of treatment. Laboratory experiments will be conducted at the University of Delaware to quantify the ability of biochar and ZVI to remove nitrate and phosphorus. A field study will be conducted by the University of Virginia in conjunction with the City of Charlottesville, VA, where biochar and ZVI will be used as amendments in a bioinfiltration facility. Soils and stormwater characteristics selected for the laboratory study will match those for the field site. Data from the biochar/ZVI treatment system will be compared with a field study using biochar alone supported by the National Fish and Wildlife Federation in Delaware, and a pilot-scale system employing biochar separate from ZVI, supported by the Delaware Department of Transportation. Results will be shared with managers in transportation agencies, e.g., Delaware Department of Transportation and Maryland Transit Administration, whom the principal investigators (PIs) have established relationships with through ongoing projects.